For instance, Roman politician from overseas in Ireland (6)
I believe the answer is:
empire
'for instance roman politician' is the definition.
I can't judge whether this definition defines the answer.
'overseas in ireland' is the wordplay.
'overseas' becomes 'mp' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'ireland' becomes 'eire' ('Eire' can be a synonym of 'ireland').
'mp' going into 'eire' is 'EMPIRE'.
'from' is the link.
Can you help me to learn more?
(Other definitions for empire that I've seen before include "Former British-ruled countries" , "Over which 23 down rules" , "Wide dominion" , "See 5" , "Multinational" .)